Add Support to mimic CDN providers

This PR adds support to mimic CDN provider API calls. While this might not fit in the scope of Mimic (since this does not mock Openstack endpoints, but is aimed at mocking Fastly API calls), the intent of this PR is to get feedback on if this is the right approach. If this turns out to fit into the Mimic context & can be merged, I can clean up this PR & add tests.
As we've been discussing on IRC and elsewhere, this is not a terribly scalable strategy for adding new resources.

Here's a though - what if we made this fastly mock a "regular" mock, in that it implemented `IAPIMock` and got an automatically-allocated API prefix, but returned `[]` from its `catalog_entries` method?  Nothing should be hard-coded to find the fastly API at `/fastly` in your real code, so presumably all these links are going to come back from ... something.  Or do you configure a fastly endpoint and `localhost:8900/fastly` is where you tell it to go?

It would be easier to discuss this if you included some documentation as to how to use it - perhaps a patch to `README.md` for now?